A DPF device of a continuous regeneration type has been known as the exhaust gas purification system for reducing the amount of the PM exhausted to the outside by trapping the PM exhausted from the diesel engine by means of a filter called the DPF, the DPF device including the DPF and a DOC (Diesel Oxidation Catalyst) provided on the upstream side of the DPF (refer to Patent Document 1, for example).
In this DPF device of a continuous regeneration type, the PM trapped in the DPF is continuously combusted and purified so that the DPF self-regenerates, when the temperature of the exhaust gas is approximately 350° C. or higher. When the temperature of the exhaust gas is low, however, it is difficult for the PM to be oxidized and for the DPF to self-regenerate since the DOC would have a lowered temperature and not be activated. As a result, the PM would be accumulated in the DPF which would be clogged up in a progressive manner, causing the problem that the exhaust pressure would be increased.
Now, when the amount of the PM accumulated in the DPF has exceeded a predetermined amount, the exhaust gas purification system regenerates the DPF by performing multistage retarded injection (multi-injection) or post-injection of a fuel into a cylinder to forcibly raise the temperature of the exhaust gas flowing into the DPF, thereby combusting and removing the PM trapped in the DPF.
The multi-injection is performed in order to raise the temperature of the DOC to a catalyst activation temperature by raising the temperature of the exhaust gas exhausted from the engine. The post-injection is performed in order to raise the temperature of the exhaust gas at the inlet of the DPF to the temperature equal to or higher than the temperature at which the PM is combusted, by supplying a large amount of unburned fuel into the exhaust gas and oxidizing (combusting) the supplied unburned fuel by the DOC.
The DPF regeneration includes automatic regeneration and manual regeneration. The automatic regeneration refers to the DPF regeneration that is performed automatically while a vehicle is in motion, and the manual regeneration refers to the DPF regeneration that is performed by the manual operation of a driver while the vehicle is stopped. In the manual regeneration, the driver is alerted when clogging in the DPF (the amount of the PM accumulated) has exceeded the predetermined amount while the vehicle is stopped, so that the DPF is regenerated when the driver presses a regeneration button.
Moreover, LLIR (Long Low Idle Regeneration) is one of the DPF regenerations performed when the vehicle has idled for a predetermined time or longer (refer to Patent Document 2, for example).
PRIOR ART DOCUMENTS
Patent Document 1: Japanese Patent No. 4175281
Patent Document 2: Japanese Patent Application Publication No. 2008-180154
Now, in the LLIR, it is difficult to calculate the amount of the PM accumulated by a distance traveled or differential pressure in the DPF since the vehicle is stopped and idling. Accordingly, the DPF is automatically regenerated upon issuing a regeneration request to the driver when a cumulated value has reached a predetermined value or higher, the cumulated value being obtained by cumulating stopped/idling time or cumulating predicted amounts of the PM accumulated that vary depending on the speed and the load of the engine.
However, in the regeneration of the DPF during the aforementioned LLIR, the stopped/idling time would be counted and cumulated even when the vehicle is temporarily stopped at the traffic light or the like or repeats stopping and moving. As a result, there arises a problem of inconvenience that the regeneration request is issued when the cumulated value has exceeded a predetermined threshold and that the frequency of the regeneration request issued is increased.
The present invention has been designed to solve the aforementioned problems, and an object thereof is to provide an exhaust gas purification system that can reduce the frequency of the DPF regeneration requests issued during the LLIR, thereby improving convenience.